A Case of an SMARCB1 (INI1)-Deficient Intrathoracic Neoplasm That Did Not Respond to Chemotherapy for Non-Small Cell Lung Cancer and Rapidly Progressed.

Introduction: SMARCB1 (INI1)-deficient intrathoracic neoplasms are rare and highly malignant. We report a case of a patient with this tumor who was initially diagnosed with non-small cell lung cancer and whose disease rapidly progressed to death despite chemotherapy. Case Presentation: A man in his 60s was diagnosed with a mass exceeding 10 cm in the lower lobe of the right lung and a right pleural effusion on the first examination. Transbronchial biopsy of the primary lesion revealed a tumor with rhabdoid features, which was diagnosed as an undifferentiated malignant neoplasm. Clinically, the patient was diagnosed with non-small cell lung cancer and was treated with carboplatin, nab-paclitaxel, durvalumab, and tremelimumab. However, at the end of the second course, there was rapid disease progression. Based on a pathological review, the tumor was considered an SMARCB1-deficient intrathoracic neoplasm. Although we considered further treatment, his general condition deteriorated, and he died about 2 months after his first visit. Conclusion: This disease is rare, and we believe that it is necessary to disseminate the concept of this disease and accumulate knowledge to establish a treatment.